Compound diffraction horn



Oct. 14, 1958 L. s. HOODWIN COMPOUND DIFFRACTION HORN 5 Sheets-Sheet 1 Filed Aug. 19, 1952 Oct. 14, 1958 s. HOODWIN COMPOUND DIFFRACTION HORN 5 Sheets-Sheet 2 Filed Aug.v 19, 1952 Oct. 14, 1958 L. s. HOODWIN COMPOUND DIFFRACTION HORN 5 Sheets-Sheet 4 Filed Aug. 19, 1952 m0 7: uWZOLmmN 2 ZQOOO a 4 5 e T s s v lqooo CYC LE3 PER SECOND a 4 5 e. 7 a s a 1,000 .FREQuENcY IN Oct. 14, 1958 s. HOODWIN 1' 2,856,467

COMPOUND DIFFRACTION HORN Filed Aug. 19, 1952 5 Sheets-Sheet 5 Patented Oct 14', 1958 2,856,467 COMPOUND DIFFRACTION HORN.

Louis S. Hoodwin, Bridgman, Mich., assignor to Electro- Voice, Incorporated, Buchanan, Mich.

The present invention-relates to a loud speaker and more. particularly to an improved loud speaker known as a compound diffraction horn.

In public address systems, industrial and announcement installations and out of doorinstallations, it has been common to use horn loud speakers. In horn loud speakers, the dispersed angle decreases as the horn size increases. The increase in horn size brings about a lower cut-off frequency, thereby accentuating the reproduction below the range of 1000 cycles. Generally, the greatest percentage of power in the driver unit also lies in the range below 1000 cycles. To use a large speaker horn or trumpet would result in a .bulky device, and hence it has been common to use folded horns either of the single or double fold type. Most of the conventional reentrant or folded public address horns, however, have many disadvantages which limit their usefulness. Perhaps the greatest disadvantage encountered is poor frequency response and narrow polar pattern. Such conventional reentrant horns of a popular size have a diam eter of twenty inches and a high frequency cut-off around 2000 to 4000 cycles. Thus, the fidelity of reproduction is limited. The limit of the high frequency response also lowers thespeech intelligibility, since a cut-off at an upper frequency limit of 3500 cycles per second reduces the articulation index by twenty percent.

The deficiencies of the conventional reentrant or reflex public address horns are primarily due to two causes. First, it is difficult to design a driver unit that will reproduce both the low frequencies from 100 cycles per second to 1000 cycles per second and the higher frequencies up to 10,000 cycles per second with the same efficiency using a common throat, since the high frequencies require a smaller throat than the low frequencies. Furthermore, the dimensions across the air columns at the ends of a reentrant horn are larger than one-half wave length the frequency to reproduced, and hence produce a destructive interference which reduces the high frequency output. This fact is primarily present beyond 3500 cycles per second. Due to the narrow polar pattern, it has been common to use clusters of horns in order to get adequate coverage if the audience is dispersed laterally.

The quality of reproduction of the conventional reentrant or reflex horn suffers greatly because its principal response is in a range from 1000 to 3000 cycles per second, and the base response is generally poor. An attempt to obtain adequate base response for acceptable quality produces a horn which is too large and bulky for easy handling, and further such a horn is relatively expensive. In order to overcome some of the disadvantages of the conventional horns, an attempt has been made to use two concentric folded horns, driven by two driver units, one a tweeter of conventional design and the other a woofer comprising a cone speaker. The cone speaker, however, has the disadvantage of being subject to the effects of humidity and is not readily adaptable to outdoor installations. Such an arrangement, furthermore, is appreciably more expensive because of the need for two driver units and a cross-over network. I

In order to overcome some of the disadvantages encountered by the more conventional public address horns it is proposed in accordancewith the present invention to devise a compound diffraction horn wherein a single driver unit has its diaphragm coupled on one side to a folded or reentrant low frequency horn and its other side coupled to a high frequency horn. The driver unit is so designed that the proper throat size is available for maximum efficiency of each horn in the range of frequencies to be covered thereby. In order to obtain maximum base response with a minimum of size and expense, the low frequency horn is made with a cycle per second taper and a comparatively small mouth. The mouth of the horn of the unique configuration offers some advantages not heretofore obtained. If this horn is used in theopen area away from other structures, its low frequency response is comparable to that of the more conventional horn where the base response begins to drop rapidly. T he present horn, however, continues to reproduce still lower frequencies, although some reflection irregularities occur due to the small size of the mouth. If the mouth of the horn is mounted next to a wallor other flat surface, the effect is to increase the mouth size. Thus, it is possible to utilize the acoustic loading properties of the location which heretofore has not been possible in the more conventional structures. Where added base response is desired in an open space, this may be accomplished by using two or more horns fastened together to provide mutual loading.

The low frequency horn contemplated by the present invention has a generally rectangular outline with an improved polar response along its longer dimension. Provision is made for mounting the horn either vertically or horizontally. If a more concentrated polar pattern is desired, the longer dimension is arranged horizontally.

It is, therefore, an object of the present invention to provide an improved compound diffraction horn having an extended range of frequency reproduction.

Another object of the invention is to provide a compound diffraction horn speaker having an improved or extended dispersement of sound.

Still another object of the invention is to provide an improved loud speaker having improved polar response characteristics.

A further object of the invention is to provide an improved driver unit for a compound horn speaker.

Still another object'of the invention is to provide a horn loud speaker which can be arranged in various groups or configurations to obtain particular dispersemeut char acteristics.

A still further object of the invention is to provide an improved speaker driver unit wherein a single diaphragm of the driver unit efficiently drives its horns having different frequency characteristics.

Still another object of the present invention is to pro vide an improved compound diffraction horn speaker having a driver unit which is Weatherproof.

Other and further objects of the present invention subsequently will become apparent by reference to the following description taken in conjunction with. the accompanying drawings, wherein:

Figure l is a perspective view of a compound diffraction horn embodying the present invention;

Figure 2 is a sectional view taken along. the longitudinal axis of the horn shown in Figure 1;

Figure 3 is a sectional view taken along the axis of the driver unit;

Figure 4 is a sectional view taken along the line 44 of Figure 2;

Figure 5 is a partial sectional view taken along the line 55 of Figure 2;

Figure 6 is a sectional view taken along the line 66 of Figure 3;

Figure 7 is a plan view of the device shown in Figure 1;

Figure 8 is a polar radiation pattern illustrating the characteristics of the prior art structures;

Figure 9 is a graphical representation showing the response curves obtained by the present device as contrasted to those commonly obtained by the prior art structures;

Figure 10 is a polar radiation pattern illustrating the characteristic response of a horn constructed according to the present invention;

Figure 11 is a plan view of a horn grouping obtainable by a plurality of the loud speakers of the present invention;

Figure 12 is another view of a diflerent horn groupmg;

Figure 13 is a front view of the horn grouping shown in Figure 12;

Figure 14 is a front view of still another grouping of units possible by a combination of a plurality of devices constructed in accordance with the present invention;

Figure 15 is a plan view of still another grouping of loud speakers; and

fastening means such as a rivet 39. The member 38 has a cylindrical recess 41 which is engaged by the smaller end of the frusto-conical member 26. Within the smaller end of the frusto-conical member 26 are positioned two radially inwardly extending fins 42 which engage notches in the larger end of the frusto-conical member 27. The support structure 38 has two radially extending members 43 which engage suitable notches in the larger end of the frusto-conical member 25.

Figure 16 is a front view of the grouping shown in Figure 15.

A compound diffraction horn embodying the principles of the present invention is illustrated in Figures 1, 2 and 7 of the drawings. It will be noted that the compound d-iifraction horn comprises a driver unit 21 connected to a high frequency or tweeter horn 22 and a low frequency folded or reentrant born 23.

The reentrant horn 23 comprises an outer bell member 24 within which is supported the folded or reentrant horn portions formed by a plurflity of members 25, 26 and 27 held in position by suitable supporting structures. While the members 25, 26 and 27 are sections of an exponential horn, they appear frusto-conical in the drawings and will be referred to henceforth as frusto-conical members. At the rear of the bell member 25 there is provided an enclosure 28 for the purpose of housing a suitable transformer or matching network. The outer bell member 24 at opposite sides is provided with a plurality of bosses 29 for receiving supporting brackets. Where a single horn is employed, the bosses 29 are engaged by the supporting brackets in order to mount the bell 23 with its longer dimension vertically. Another pair of bosses 31 are provided for receiving the brackets or supporting structures where a single horn is to be mounted with its longer dimension horizontally. These bosses 29 and 31 are also utilized for combining a plurality of horn units into an array or horn cluster, or other desired grouping, as subsequently will become apparent.

The manner in which the frusto-conical members 25, 26 and 27 are supported Within the bell 24 is best understood by referring to Figures 2, 4 and 5 of the drawings. At an intermediate point in the bell member 24 there is provided a drive unit mounting means having a vertical member 32 and a horizontal member 33 carrying at its intersection a supporting structure which has a threaded circular portion carrying a boss 34 which is engaged by a portion of the driver unit 21. The boss 34 extends into a reduced diameter portion 35, or rim, which engages the smaller end of the frusto-conical member 27. The vertical and horizontal members 32 and 33 also carry an annular member 36 which receives the smaller end of the frusto-conical member 25. Within the smaller end of the frusto-conical member 25 two projecting fins 37 eX- tend radially inwardly. The larger end of the frustoconical member 26 is provided with two notches which are engaged by the fins 37 to hold that end in position.

At the rear of the bell member 24 there is mounted a support structure 38 retained in position by a suitable The enclosure or transformer housing 28 is secured to the rear of the bell member 24 by suitable screws 44. The housing 28 at its rear is provided with a boss 45 or other structure which has a threaded opening 46 for receiving a fastening bolt or cap screw.

The driver unit which is shown in Figure 3 has certain features which insure proper operation and eflicient driving of both horn units. The driver unit 21 has a casing or housing 47 and a cap or cover 48. The casing 47, which is generally cylindrical, has an axial passage formed by an opening 49 in the bottom of the casing 47 and an opening 51 in the top of the casing. Adjacent to the opening 49 there is secured a threaded cylindrical member 52 which engages the threaded opening within the boss 34 of the supporting structure 32. The axial Passage through the casing 47 is further defined by a permanent magnet 53 having a central passage. The permanent magnet at its narrower end defines an annular member 54 in which the opening 51 has been formed. The annular member 54 is surrounded by another annular member 55 so as to provide an annular air gap for the diaphragm and the voice coil. A suitable screen 56 covers the opening 51 to prevent any foreign matter from passing therebeyond which otherwise might become lodged in the annular air gap. One side of the annular air gap is furthermore protected by an annular structure 57 which has an inner rim 58 engagng the underside of the annular pole piece extension member 54. The outer rim 59 of the annular member 57 engages the underside of the annular member 55. Immediately beyond the annular member 55 there is positioned a spacing washer or ring 61 which engages the peripheral portion of the diaphragm support ring 63. The other side of the diaphragm support ring is engaged by another ring or washer 64 which in turn is engaged by the cover 48 retained in position by a plurality of screws or bolts 65. The diaphragm support structure 63 is connected to the diaphragm which has a cylindrical portion 66 provided with a plurality of apertures 67. The annular diaphragm portion 66 extends into the air gap voice coil 68 between the annular members 54 and 55 of the housing. This portion of the annular diaphragm member 66 carries the voice coil 68. The diaphragm structure is completed by a domed concave convex member 69.

Just beyond the domed structure 69 of the diaphragm is a frusto-conical member 71 held in position by three projecting legs 72 which engage the inner surface of the cover member 48. The frusto-conical member 71 has a concave inner surface of slightly larger but generally complementary dimensions corresponding to the curvatures of the top of the domed member 69 of the diaphragm. The frusto-conical member 71 along the axis of the speaker has a frusto-conical throat 73, the outer edge of which is engaged by a protective screen 74 which extends to the inner surface of the cover 48.

The cover 48 is provided with a plurality of inclined holes or passages 75 terminating in countersunk recesses 76 for the removal of condensate or moisture. It will be noted that the cover 48 has a reduced diameter threaded portion 77 which engages the threaded inner surface of the horn 22. From Figure 6 it will be noted that the cover 48 is provided with a plurality of binding posts or electrical connections 78 which are connected to the voice coil 68 in the conventional manner.

Those skilled in the art will note that the construction shown in Figure 3 differs from the conventional structure inseveral different ways. Since the loud speaker assembly shown in Figure 2 is intended to be used for all installations whether indoor or outdoor, the cover 48 has beenv provided with moisture removing drainage passages 75.

The concave frusto-conical member 71 is unique in that it has the frusto-conical axial passage 73 which is for the purpose of delivering frequency components of appreciable magnitude within the range from 8000 to 10,000 cycles per second. The passageway 70in the cover 48 also transmits frequencies in the range from 1200 to 10,000 cycles per second which are taken off primarily in the peripheral portion of the domed structure 69 of the diaphragm. The axial passage through the magnet 53 to the folded or reentrant horn transmits frequencies up to 1500 cycles per second, although the folded horn has its principal efficiency in the range from a little more than 1000 cycles per second down to 100 cycles per second.

The tweeter horn 22 radiates frequencies over the rangev from 1200 to. 10,000 cycles per second. The holes 67 in the annular portion 66 of the diaphragm are provided to reduce the effective inductance of the diaphragm. The annular member 57 is provided not only to protect the annular air gap, but also to limit the volume of air to the left of the diaphragm support 63 so that the proper diaphragm impedance is obtained. The diaphragm preferably is molded of phenolic resin and glass cloth since the glass cloth fibers have a very high tensil strength and fatigue resistance. The voice coil 68 is made of edge wound copper ribbons on a Duralumin form.

In Figure 8 there has been shown a polar radiation pattern which is characteristic of the more conventional reentrant horns commonly in use. When this is compared with the polar radiation pattern in Figure 10 which is that obtained by the present compound diffraction horn, it is apparent that there is a much wider angular response. A'reference to the curves in Figure 9 also shows an overall improvement in the frequency response. The dotted line curve is characteristic of the more conventional folded reentrant or reflex loud speakers. The solid line curve is that obtained by the compound diffraction horn constructed in accordance with the principles of the present invention.

In the preferred embodiment of a present invention, the bell mouth of the member 24 has a dimension of about ten inches by twenty inches as contrasted to the twenty inch circular diameter of' the conventional reentrant horn. The compound diffraction horn has a low frequency cut-off of 100 cycles as contrasted to 150 cycles for the conventional reentrant horn. The embodiment in the high frequency cut-ofi and the polar response is graphically illustrated by the representation in Figures 8, 9' and 10.

The unique configuration of the bell member 24lends itself particularly for certain installations, such as those illustrated in Figures 11 through 16. In Figure 11, seven speakers are arranged on a circular support 81, and the covers 28 are connected together by a ring 82. Such an installation is suitable for the center of an arena or stadium. Where such coverage is not needed, a partial array comprising three horns such as that shown in Figure 12 may be employed. There an arcuate support member 83 engages the bosses 29 of the bell members 24, and when greater rigidity is required, another similar member to that shown at 83 may be used to engage the bosses on the top side. The inner ends of the housings 28 are connected to an arcuate member 84. Where the housings 28 are not needed, an arcuate member similar to 84 is used to interconnect the rivet members 39 which may be of the hollow internal thread type.

Where both vertical and horizontal dispersion is de-.

sired, it is possible to arrange the speakers as illustrated in Figure 14. Still another arrangement of speakers is represented by the showing in Figures 15 and 16. In such arrangements, the low frequency responses are improved because of the mutual loading effect. It has been found thattinstallations ofthe types suggested easily obtain'an articulation index of one. This. is. accomplished by the extension of the reproduction inexcess of 7000 cycles, as isv apparent from Figure 9. The extended high frequency range also makes the speaker particularly suitable for the clear reproductionof music.

While the preferred use of the driver unit is with the low-frequency and high frequency horn units, it is possible to use. the driver unit to augment existing loud speaker installations. The complete compound horn may be utilizedwith awoofer and a cross-over network as low as 200cycles-to obtain a high quality full range system. The driver unit and the high frequency horn may be used in combination as a tweeter for a two or three way system with a 1500 cycle crossover. If a limited concentrated high frequency response, similar to the conventional reentrant horn is desired, this may be obtainedby using only the low frequency horn and the driver unit, and driving the low frequency horn from. the high end of the driver. unit.. For special low frequency effects, a low frequency horn may bedriven only from the low frequency side of the driver unit whereupon the high frequency horn is not employed. It, therefore,.becomes apparent that in addition to obtaining an improved response characteristic andwider radiation pattern, the components of the compound diffraction horn are susceptible to additional special uses.

While for the purpose of illustrating and describing the present invention certain preferred embodiments have been shown in the drawings, it is to be understood that the invention is not to be limited thereby since such variations in the embodiments illustrated and such other combinations are contemplated as may be commensurate with the spirit and scope of the invention set forth in the accompanying claims.

I claim as my invention:

,1. A triple folded horn comprising anopen bell memberv having its edges in four planes at right angles to each other, one pair of edges being curved and of greater length than the other pair of edges, and a plurality of frusto-conical members of lesser length than said bell member arranged coaxially along the longitudinal axis of said bell member, a dynamic driving unit coupled to the smallest frusto-conical member, and means on the exterior of said bell member for securing a plurality of horns in a polygonal figure with at least one free edge of one horn in abutment with the free edge of the adjacent horn.

2. A triple folded horn comprising an open bell member having its edges in four planes at'right angles to each other, one pair of parallel edges being curved and greater in length than the remaining edges, and a plurality of frusto-conical members of lesser length than said bell member arranged coaxially along the longitudinal axis of said bell member, a dynamic driving unit coupled to the smallest frusto-conical member, and means on the exterior of said bell member for securing a plurality of horns in rows with the free edges of said horns in abutment with adjacent horns.

3. A driver unit for a loud speaker horn comprising a magnetic circuit for a permanent magnet provided with an axial passage therethrough, an annular air gap in said circuit, a diaphragm having a voice coil located in said air gap, a loading plug mounted adjacent one side of said diaphragm, said plug having a concave surface and a frusto-conical surface, a flared axial passage interconnecting said concave surface with said frusto-conical surface, means for coupling a rectangular bell horn to selected portions of the diaphragm surface adjacent said plug, and means for coupling another rectangular bell horn to the entire other side of said diaphragm through the axial passage in said permanent magnet.

4. A driver unit for a loud speaker horn comprising a permanent magnet magnetic circuit provided with an axial passage therethrough and an annular air gap coaxial with said passage, a diaphragm having a voice coil located in said air gap, a loading plug mounted adjacent one side of said diaphragm, said plug having a concave surface and a frusto-conical surface, a flared axial passage interconnecting said concave surface with said frusto-conical surface, a housing for said diaphragm including means for coupling a horn having a rectangular bell to the peripheral and central portions of the diaphragm surface adjacent said plug, and means for coupling another horn having a rectangular bell and different frequency characteristics to the entire other side of said diaphragm through the axial passage, said horn bells being coaxial.

5. A dynamic driver unit for a loud speaker horn comprising a permanent magnet magnetic circuit provided with an axial passage therethrough and an annular air gap coaxial with said passage, a diaphragm having a voice coil located within said air gap, a member mounted adjacent one side of said diaphragm h 'ving a concave surface and an outer frusto-conical surfatl, a flared axial passage interconnecting said concave surface with said frusto-conical surface, a housing for said diaphragm including means for coupling a high frequency horn to the diaphragm surface adjacent said member, said housing forming a chamber about said diaphragm, said housing having at least four relatively small air passages extending from within said chamber at the edge of said diaphragm to the exterior of said housing, said passages being arranged at regular intervals in a circle.

6. A triple folded compound diffraction horn comprising an open bell member having a rectangular cross section with the longer pair of edges curved, a plurality of exponential frusto-conical members of lesser length than said bell member arranged coaxially along the central axis of said bell member, said frusto-conical members and said bell member having a flare cut off of 100 cycles per second, a dynamic driving unit coupled to the smallest frusto-conical member on one side of its diaphragm and on the other side of its diaphragm to a single open bell member of rectangular cross section located within said first bell member, and a boss on each side of the exterior of said first bell member for receiving mounting members to secure a plurality of horns in abutment with each other for mutual loading of a plurality of horns with at least one free edge of one horn in abutment with a similar free edge of an adjacent horn.

7. A triple folded compound diffraction horn comprising a first open outwardly flaring bell member having a rectangular cross section, a plurality of frusto-conical members of lesser length than said bell member arranged coaxially along the central axis of the first bell member,

and a driving unit having a diaphragm coupled to the smallest frusto-conical member on one side of its diaphragm and on the other side of its diaphragm to a second open outwardly flaring bell member of rectangular cross section located within the open end of the first bell member.

8. A triple folded compound diffraction horn comprising a horn member flaring outwardly from a closed end to an open end, a drive unit mounting means mounted to the horn member between the open and closed ends thereof having a circular portion normally disposed coaxially about the center line of the horn, said circular portion having a central aperture and two spaced coaxial rims extending toward the closed end of the horn member, said circular portion also being provided with a plurality of fins between the coaxial rims extending toward the closed end of the horn member and having a notch confronting the closed end of the horn member, means located at the closed end of the horn memher for mounting three frusto-conical members, and three frusto-conical members of three difierent sizes disposed coaxially between said mounting means and the circular portion of the drive unit mounting means, the smaller, ends of the larger and smaller of said frustoconical members abutting the larger and smaller rims of the circular portion, respectively, and the larger end of the intermediate size frusto-conical member having notches therein accommodating the notched portions of the fins of the circular portion.

9. A triple folded compound diffraction horn comprising the elements of claim 8 wherein the means located at the closed end of the horn member for mounting three frusto-conical members comprises a circular member having a recess therein confronting the open end of the horn member and a plurality of notched fins extending from the recess, the smaller end of the intermediate sized frusto-conical member having slots therein accommodating the fins and being secured within the recess, and the larger end of the smallest frusto-conical member having notches therein mating with the notched portions of the fins, said mounting means having a plurality of ribs extending radially outward from the circular portion having a notch at their ends, the larger end of the larger frusto-conical member having notches therein mating with the notched portion of the ribs.

10. A loud speaker comprising the elements of claim 8 wherein the circular portion of the drive unit mounting means is provided with a threaded annular recess coaxial with the aperture therein and confronting the open end of the horn member, and a drive unit having an outwardly extending hollow cylindrical sound carrying member threadedly engaged within the recess.

11. A triple folded compound diffraction horn comprising a drive unit having a magnetic circuit provided with an axial passage therethrough and having an annular air gap, an annular diaphragm having a cylindrical edge located in said air gap, a voice coil secured to the cylindrical edge of the diaphragm, a loading plug mounted adjacent to one side of the diaphragm having a concave surface confronting the diaphragm and a frusto-conical surface remote from the diaphragm, a flared axial passage interconnecting the concave surface with the frusto-conical surface, a first rectangular bell horn mounted adjacent to the flared axial passage, a second open bell horn of rectangular cross section disposed about the drive unit and first bell horn, a plurality of frusto-conical members arranged coaxially within the second bell horn along the central axis thereof, the smallest of said frusto-conical members being connected to the axial passage in the magnetic circuit of the drive unit.

References Cited in the file of this patent UNITED STATES PATENTS 1,625,325 Macartney Apr. 19, 1927 1,653,144 Bach Dec. 20, 1927 1,715,057 Decaux May 28, 1929 1,723,570 Lyon Aug. 6, 1929 1,750,900 Minton et a1 Mar. 18, 1930 1,768,226 Williams June 24, 1930 1,930,915 Wente Oct. 17, 1933 2,206,427 Preston July 2, 1940 2,251,148 Buell Sept. 5, 1950 2,537,141 Klipsch Jan. 9, 1951 2,568,883 Carrington Sept. 25, 1951 FOREIGN PATENTS 246,634 Great Britain Feb. 4, 1926 OTHER REFERENCES A Compound Horn Loudspeaker, by Olson et al., in I. A. S. A., July 1936, pages 4852.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,856,467 October 14,. 1958 Louis S I-Ioodwin Column 3, line 63, strike out "circular portion carrying a" and insert the same before "threaded" in line 62, same column; column 8, line 62, list of references cited under "UNITED STATES PATENTS", for

Sept. 5 read 2,521,148 Buell Sept. 5, 1950 Signed and sealed this 17th day of February 1959.

SEAL) 11156815:

KARL H. AXLINE Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,856,467 October 14,. 1958 Louis S a Hoodwin It is hereby certified that error appears in the printed specification of the above nu mbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 63, strike out "circular portion carrying a" and insert the same before "threaded in line 62, same column; column 8, line 62, list of references cited, under "UNITED STATES PATENTS" for 2,251,148 .Buell Sept. 5, 1950 read 2,521,148 Buell mm Sept. 5, 1950 Signed and sealed this 17th day of February 1959..

SEAL) ttest:

KARL H. AXLINE Commissioner of Patents 

